Differential mechanisms commonly used on vehicles are of the sun and planet gear type and have a well known disadvantage that when one wheel is on a slippery surface such as mud or ice and the other wheel is on a firm surface capable of providing traction, the first wheel will simply spin as it receives all the available power transmitted to the differential.
Limited slip differential mechanisms have been proposed in an attempt to overcome this problem which restrict the extent to which one wheel can spin relative to the other but such differentials are more complex and, therefore, most costly to produce.
In European patent application EP-A-0326289 there is proposed an alternative differential mechanism comprising two output cam members rotatable about an axis, each said member having a single frustoconical cam surface thereon of undulating from comprising pairs of mutually inclined surfaces, and a plurality of cam followers having end surfaces engaging the cam surfaces of the output cam members, the arrangement being such that relative contra rotation of said output cam members causes the cam followers to slide axially, and an input member engaging the followers which are slidably supported by the input member and moving the followers circumferentially relative to the output cam members.
Such a differential will hereinafter be called a differential of the type referred to.